Materials Express - Ingenta Connect

IP: 5.10.31.210 On: Thu, 29 Sep 2022 08:48:04Copyright: American Scientific Publishers

Delivered by Ingenta

Materials ExpressArticle

Copyright © 2021 by American Scientific PublishersAll rights reserved.Printed in the United States of America

2158-5849/2021/11/533/007doi:10.1166/mex.2021.1934

www.aspbs.com/mex

An one-pot approach to hierarchical flower-likeBi2O2CO3/Bi2WO6 heterojunctions: Self-assembly,in situ carbonization, and enhanced visible lightphotocatalytic activitiesHaibin Li∗, Peng Jiang, Jian Zhang, Xiang Luo, and Ziwen Long

School of Materials Science and Engineering, Changsha University of Science and Technology,Changsha 410114, PR China

ABSTRACT

Large specific surface areas and well-defined interfaces are the keys to improving the photocatalytic activitiesof heterojunction photocatalysts. In the present paper, hierarchical flower-like Bi2O2CO3/Bi2WO6 heterojunc-tions were prepared via an one-pot hydrothermal approach using Bi(NO3)3 ·5H2O and Na2WO4 ·2H2O as rawmaterials. SDS was used as a structure directing agent. The selective adsorption of SDS on the (001) planesof Bi2WO6 leads to the formation and self-assembly of Bi2WO6 nanosheets, resulting in hierarchical flower-likestructures. The generation of Bi2O2CO3 is attributed to the in-situ carbonization of Bi2WO6 by CO2−

3 producedby the decomposition of precipitant urea, forming well-defined Bi2O2CO3/Bi2WO6 interfaces. The flower-likeBi2O2CO3/Bi2WO6 heterojunctions showed enhanced photocatalytic activities for MB degradation, which wasmainly due to their large specific surface areas and electric-field-assisted charge transfer at the heterojunctioninterfaces. The possible photocatalytic mechanism was proposed based on the experimental results and bandstructures.

Keywords: Bi2WO6, Bi2O2CO3, Heterojunction, Self-Assembly, Hydrothermal Synthesis, Photocatalysis.

1. INTRODUCTIONAs an advanced technology, photocatalysis has attractedsignificant attention as it is expected to solve problemsof environmental pollution and energy shortage. SinceFujishima and workers reported the photo-splitting of H2Ointo H2 and O2 using TiO2 [1], more and more research hasbeen focused on the preparation, modification, and prop-erties of photocatalysts [2].In recent years, considerable attention has been paid

to Bi2WO6 due to its narrow band gap (2.8 eV), chemi-cal stability, and effective use of sunlight [3–6]. However,

∗Author to whom correspondence should be addressed.

the low quantum efficiency caused by the high recombi-nation of electrons and holes hinders its practical appli-cation. There have been considerable efforts to solve thisproblem with ion doping [7], noble metal loading [8],semiconductor combination [9–14] and morphology con-trol [3–6]. Among these strategies, shape controllable syn-thesis is valuable for Bi-containing photocatalysts as thephotocatalytic properties are strongly dependent on theirmorphologies and microstructures [3–6]. Photocatalystswith three-dimensional hierarchical flower-like structurescomposed of nanosheets have proven to show enhancedactivity due to their hierarchical porous structures, goodpermeability, high light-harvesting capacity, and higheramounts of surface active sites [3–6]. Semiconductor

Mater. Express, Vol. 11, No. 4, 2021 533

http://www.aspbs.com/mex



Materials ExpressAn one-pot approach to hierarchical flower-like Bi2O2CO3/Bi2WO6 heterojunctions

Li et al.

Article

combination is also considered as an effective way sincethe formed heterojunction promotes the separation of elec-trons and holes [9–14]. A variety of semiconductors, suchas BiVO4 [9, 10], CsPbBr3 [11], g-C3Nx [12], Ta3N5 [13],Cu2S [14], and Bi2O2CO3 [15], has been adopted to mod-ify Bi2WO6. Bi2O2CO3 is a typical Sillén-phase layer com-pound with a band gap of 3.1 eV. Zhao [16] and Liu [17]have reported its excellent photocatalytic performances fororganics degradation. It has attracted increasing interest forusage in forming Bi2O2CO3/Bi2WO6 heterojunction pho-tocatalyst due to its unique electronic structure and bandstructure, which is matched to that of Bi2WO6 [15, 18].As reported previously, the photocatalytic activity of het-erostructure photocatalysts depend on not only the photo-stability of each component in the heterostructures but alsothe effective contacts between them [9–15]. Therefore, itis important to fabricate Bi2O2CO3/Bi2WO6 heterostruc-tures with well-defined interfaces formed by the close andeffective contacts between two semiconductors.In this work, Bi2O2CO3/Bi2WO6 heterojunction pho-

tocatalysts with 3D hierarchical flower-like morphologywere prepared by an one-pot hydrothermal approach inorder to achieve large specific surface areas. Bi2O2CO3 isformed via an in situ carbonization of Bi2WO6 on its sur-face so as to form well-defined Bi2O2CO3/Bi2WO6 inter-faces. The photodegradation of methyl blue (MB) undervisible light irradiation was investigated to evaluate thephotocatalytic activity of the samples.

2. EXPERIMENTAL DETAILS2.1. Materials and SynthesisAll chemicals were of AR grades and used without furthertreatments. Bi2O2CO3/Bi2WO6 heterojunction photocata-lysts were synthesis by an one-pot hydrothermal process.In a typical procedure, 2 mmol of Na2WO4 · 2H2O and4 mmol of Bi(NO3)3 · 5H2O were dissolved in 65 mLof distilled water and 15 mL of acetic acid, respectively.A suspension was then obtained by mixing the abovetwo solutions together and a certain amount of urea (2.5,5.0, 7.5 and 10.0 g) and 0.5 g sodium dodecyl sulfate(SDS) were added. The suspension was transferred intoan 100 mL Teflon-lined autoclave after 30 min of stirringand then heated at 140 �C for 20 h. After the autoclavewas naturally cooled to room temperature, the sampleswere collected, washed with distilled water and anhydrousethanol for 3 times, respectively, and then dried at 80 �Cfor 20 h.

2.2. CharacterizationXRD analysis was carried out by a Rigaku D/Max 2500powder diffractometer (XRD) with Cu K� radiation (�=1.5406 Å). The morphologies and microstructures of thesamples were analyzed by field-emission scanning electronmicroscopy (FESEM, FEI SIRION 200) and transmissionelectron microscopy (TEM, Philips Tecnai20G2S-TWIN).

The BET surface areas of the as-prepared samples weredetermined with a Micromeritics ASAP2020 equipment.UV-vis diffuse reflectance spectra (UV-vis) of the sam-ples were obtained with a Specord 200 UV spectropho-tometry. The photoluminescence (PL) measurements wereperformed on a Hitachi F-4500 fluorescence spectropho-tometer at room temperature.

2.3. Photocatalytic TestThe photodegradation of MB aqueous solution wasinvestigated to evaluate the photocatalytic activities ofthe Bi2O2CO3/Bi2WO6 heterojunctions with a Xe lamp(125 W, with a 410 nm cut-off filter) as light source. Theexperiments were carried out at room temperature in alaboratory-made photoreactor as follows: 0.05 g of pho-tocatalyst was dispersed in 50 mL MB solution with aconcentration of 10 mg ·L−1. Before irradiation, the sus-pension was magnetically stirred for 30 min in the dark toreach an adsorption/desorption equilibrium between MBand photocatalysts. At regular intervals, 5 mL of suspen-sions were collected and centrifuged to remove the photo-catalyst. UNICO UV-2100 spectrophotometer was used todetermine the concentration of MB solution by monitoringthe absorbance at 665 nm.

3. RESULTS AND DISCUSSIONThe XRD patterns of the samples prepared at variousurea consumptions were shown in Figure 1. When theamount of urea was controlled at 2.5 g, all the diffractionpeaks of the as-prepared sample could be readily indexedto that of a pure orthorhombic phase of Bi2WO6 (JCPDScard no. 73-2020). With the amount of urea increases to5.0, 7.5 and 10.0 g, respectively, four characteristic diffrac-tion peaks at 2� = 13�, 24�, 30�, and 39� assigned toBi2O2CO3 (JCPDS no. 41-1488) appeared, suggesting thattiny amounts of Bi2O2CO3 coexisted with Bi2WO6 in theproducts and the co-growth of Bi2O2CO3 and Bi2WO6

could be achieved by such an one-pot hydrothermal pro-cess. The mass fractions of the Bi2O2CO3 in the sampleswere 0.09, 0.18 and 0.31 for the samples prepared at ureaconsumptions of 5.0, 7.5 and 10.0 g, respectively, whichwere estimated from XRD intensity data by using the for-mula as expressed by Eq. (5):

RC = ICIC + IW

(1)

where IC and IW are the integrated intensity of Bi2O2CO3

(013) and Bi2WO6 (113) diffraction peaks, respectively.Figures 2(a)–(f) show the SEM images of the sam-

ples with Bi2O2CO3 mass fractions of 0, 0.09, 0.18 and0.31, respectively. Evidently, all the samples are hierar-chical flower-like microspheres with an average diame-ter of 1.5–2 mm. The morphologies of the samples donot show much change, although the urea consumption

534 Mater. Express, Vol. 11, pp. 533–539, 2021



Materials ExpressAn one-pot approach to hierarchical flower-like Bi2O2CO3/Bi2WO6 heterojunctionsLi et al.

Article

Fig. 1. XRD patterns of the samples prepared at different ureaconsumptions.

varies. It can be seen from the magnified SEM imagesof Figures 2(b) and (d) that nanosheets with a thicknessless than 50 nm are interlaced helically and loosely form-ing hierarchical flower-like microspheres with open porousstructures, leading to a larger surface area and the facilita-tion for the entry of reactants and the release of products.The BET surface areas of the samples with Bi2O2CO3

mass fractions of 0, 0.09, 0.18 and 0.31 are 31.4, 31.2,

Fig. 2. SEM images of the samples with various Bi2O2CO3 mass frac-tions of (a, b) 0, (c, d) 0.09, (e) 0.18 and (f) 0.31.

30.9, and 30.2 m2 · g−1, respectively. Moreover, the hier-archical structure is beneficial for light absorption andrefraction, resulting in a higher light harvest.Figure 3 shows the SEM image of the sample prepared

at the urea consumption of 2.5 g in the absence of SDS.It can be seen that the products are composed of stackednanosheets, which is totally different from the samplesobtained in the presence of SDS. The BET surface areasof the sample was determined to be 5.2 m2 · g−1. Theseresults indicate that SDS is the key factor for the formationof the hierarchical flower-like structure.TEM and high magnificent TEM (HRTEM) were

applied to further investigate the microstructure of theas prepared sample with a Bi2O2CO3 mass fraction of0.18. It can be observed from Figure 4(a) that the sampleexhibits a flower-like hierarchical structure with a diam-eter of 2 mm, which is consistent with the SEM results.Figure 4(b) is the HRTEM image of the marked areain Figure 4(a), which reveals the polycrystalline struc-ture of the sample. In Figure 4(b), the lattice spacingmeasured to be 0.192 nm and 0.185 nm are assignedto the interplanar spacing of the Bi2WO6 (220) planeand the Bi2O2CO3 (022) plane, respectively, suggest-ing that the nanosheets are actually formed by the ori-ented attachment of plenty of Bi2WO6 and Bi2O2CO3

nanoplates. The obvious interfaces between Bi2WO6 andBi2O2CO3 nanoplates presented in Figure 4(b) illustratedthat well-defined Bi2O2CO3/Bi2WO6 heterojunction struc-tures are formed, which is believed to be beneficial to theimprovement of photocatalytic activity.To explore the growth process of the flower-like

Bi2O2CO3/Bi2WO6 microspheres, XRD (Fig. 5) and SEM(Fig. 6) were applied to observe of the products obtainedat the urea consumption of 7.5 g at various hydrother-mal reaction stages of 0 h, 10 h and 20 h. As indicatedby the results, the product obtained without hydrother-mal treatment consists of amorphous nanoparticles (Figs. 5and 6(a)). While the product obtained after 10 h ofhydrothermal reaction are Bi2WO6 nanosheets with diam-eters of 1–3 �m and thicknesses of less than 50 nm,

Fig. 3. SEM image of the sample prepared at the urea consumptionof 2.5 g in the absence of SDS.

Mater. Express, Vol. 11, pp. 533–539, 2021 535




Li et al.

Article

(b)(a)

Fig. 4. TEM (a) and HRTEM (b) images of the as prepared samplewith a Bi2O2CO3 mass fraction of 0.18.

accompanied by a small amount of hierarchical archi-tectures (Figs. 5 and 6(b)). Well-defined flower-likeBi2O2CO3/Bi2WO6 microspheres were obtained after 20 hof hydrothermal reaction (Figs. 5 and 6(c)).Based on the SEM and TEM observations, we can infer

that the hierarchical flower-like structures of Bi2WO6 aredeveloped via a self-assembly process. As the hydrother-mal reaction is carried out, a lot of OH− is released dueto the decomposition of urea at high temperatures, leadingto the precipitation of Bi2WO6. The Bi2WO6 crystallinenuclei are produced and develop into tiny nanoparticles,then those nanoparticles are crystallized and further growinto nanoplates, which later self-assemble into nanosheetsby oriented attachment. As revealed by TEM results, thelateral surfaces of Bi2WO6 are enclosed by their (220)planes. Therefore, the top surfaces of Bi2WO6 nanoplatescan be inferred to be enclosed by their (001) planes.SDS has been used as a structure-directing agent to fab-ricate nanoparticles with anisotropic shapes because of itsselective adsorption on various crystallographic planes ofnuclei. It can be inferred from the results above that SDShas stronger interactions with Bi2WO6 (001) planes, whichleads to the formation of Bi2WO6 nanoplates. Furthermore,because of the selective adsorption of SDS on the (001)planes, the resulting nanoplates preferentially assemble inan edge-to-edge fashion rather than along (001) planesfor Bi2WO6, leading to the formation of 2D Bi2WO6

Fig. 5. XRD patterns of the products prepared at different reactiontime.

Fig. 6. SEM images of the samples prepared at (a) 0 h, (b) 10 h, and(c) 20 h.

nanosheets with larger sizes [19–21]. Due to the block-ing effect of SDS on the top surfaces, the formed Bi2WO6

nanosheets will not pile up along the [001] direction, butassemble in an edge-to-edge manner and curl up by a cer-tain title angle forming flower-like Bi2WO6 because of thelarger lattice tension [21–23]. As the hydrothermal processis prolonged, the CO2 released by decomposition of ureareacts with OH− in the solution generating CO2−

3 that thenreacts with Bi2WO6. This leads to the in situ carboniza-tion of Bi2WO6 producing Bi2O2CO3, and consequentlythe formation of Bi2O2CO3/Bi2WO6 heterojunctions withwell-defined interfaces.The UV-vis diffuse reflectance spectra of the samples

with Bi2O2CO3 mass fractions of 0 and 0.18 are presentedin Figure 7. The Bi2WO6 shows strong absorption in bothUV and visible range. The edge of absorption occurredat 459 nm. The steep spectrum suggests that the visiblelight absorption of the sample is due to the band-gap tran-sition. The Bi2O2CO3/Bi2WO6 heterojunction shows dualabsorption edges at 378 and 459 nm, which can attributedto Bi2O2CO3 and Bi2WO6, respectively. Moreover, theabsorbance in the 378–459 nm is significantly decreasedcompared to that of pure Bi2WO6 due to the large portionof Bi2O2CO3 in the composites. According to the equa-tion �g = 1239.8/Eg (where �g and Eg are the band-gapwavelength and the band-gap energy, respectively), the cal-culated band-gap energies of Bi2WO6 and Bi2O2CO3 are2.7 eV and 3.28 eV, respectively, which are in good agree-ment with the reported results [22, 23]. The calculatedconduction band edge (ECB) and valence band edge (EVB)of Bi2WO6 and Bi2O2CO3 were reported to be 0.16 eV and2.87 eV, and 0.276 eV and 3.56 eV, respectively. There-fore, the ECB and EVB of Bi2WO6 are more negative thanthose of Bi2O2CO3 [22, 23].





Article

Fig. 7. UV-vis diffuse reflectance spectra of the as-prepared sampleswith various Bi2O2CO3 mass fractions.

Figure 8 presents the degradation rate of MB as a func-tion of irradiation time in the presence of the samples withvarious Bi2O2CO3 mass fractions, as well as photolysis,under visible light irradiation. For comparison, the sam-ple prepared at urea consumption of 2.5 g in the absenceof SDS was also investigated. The results indicate thatall the samples show photocatalytic activities in responseto visible light, as the MB concentrations decrease fasterin the presence of those samples than that during pho-tolysis. The samples prepared with the assistance of SDSshow improved photocatalytic efficiency compared withthat obtained in the absence of SDS. Moreover, at anirradiation time of 180 min, MB is almost completelydegraded by the sample with a Bi2O2CO3 mass fraction of0.18, showing much higher efficiency than other samples.Generally, the surface area, light absorption capac-

ity, the separation of photogenerated electron–hole pairs,and the transporting rate of carriers are the key fac-tors that decide the overall photocatalytic activity of a

Fig. 8. The residual MB at different irradiation time for (a) photolysis,(b) the sample prepared at urea consumption of 2.5 in the absence ofSDS, and the samples prepared in the presence of SDS with variousBi2O2CO3 mass fractions of (c) 0, (d) 0.31, (e) 0.09, and (f) 0.18.

semiconductor [24]. The samples obtained in the presenceof SDS are more active than that obtained in the absencefor MB photodegradation. It should be attributed to theirlarger surface areas and stronger photoabsorption abili-ties of their flower-like hierarchical structures. Since theBi2WO6 and Bi2O2CO3/Bi2WO6 heterojunctions preparedin the presence of SDS possess similar morphologies andBET surface areas, the enhanced photocatalytic activity ofBi2O2CO3/Bi2WO6 heterojunctions may be ascribed to theefficient charge separation. Figure 9 shows the photolumi-nescence emission spectra of the as-prepared samples withvarious mass fractions of Bi2O2CO3. It can be clearly seenthat Bi2O2CO3/Bi2WO6 heterojunctions show lower fluo-rescence intensities than Bi2WO6, confirming the efficientcharge separation of Bi2O2CO3/Bi2WO6 heterojunctions.Photogenerated holes, �O−

2 , and �OH are consideredto be the major reactive species in organics photodegra-dation [25]. In order to understand the reaction mech-anism involved in the photodegradation of MB overBi2O2CO3/Bi2WO6 heterojunctions, photocatalytic exper-iments were carried out in the presence of the as pre-pared sample with a Bi2O2CO3 mass fraction of 0.18and various additives to find the specific reactive speciesthat play important roles in MB degradation, as follows:1 mmol of benzoquinone (BQ) was used as the scav-enger for �O−

2 , 1 mmol of ethylenediaminetetraacetic acid(EDTA) for holes, and 1 mmol of tertiary butanol (TBA)for �OH [26, 27]. In Figure 10, it can be seen that both BQand EDTA show negligible suppression on the degrada-tion rate of MB, while TBA exhibits a strong suppressingeffect. Therefore, it can be deduced that �OH is responsi-ble for the mineralization of MB over Bi2O2CO3/Bi2WO6

heterojunctions.According to the experimental results, we proposed

a possible mechanism for photodegradation of MBby Bi2O2CO3/Bi2WO6 heterojunction, as illustrated inFigure 11. In the present one pot approach, Bi2O2CO3

was formed via an in situ carbonization of Bi2WO6 on

Fig. 9. The photoluminescence spectra of the as prepared sampleswith various mass fractions of Bi2O2CO3.





Li et al.

Article

Fig. 10. The effects of various additives on photodegradation of MBover Bi2O2CO3/Bi2WO6 heterojunction with a Bi2O2CO3 mass fractionof 0.18.

its surface, so Bi2O2CO3 and Bi2WO6 nanocrystals wereclosely joined together, resulting in the effective het-erojunction interfaces. We believe that the electric-field-assisted charge transfer at the heterojunction interfaces isthe main reason responsible for the photocatalytic effi-ciency enhancement of Bi2O2CO3/Bi2WO6 composites,which consequently facilitates the photoexcited electron–hole separation in Bi2WO6. As mentioned above, the ECB

and EVB of Bi2WO6 are more negative than those ofBi2O2CO3, so both the CB and VB of Bi2WO6 are con-sidered at lower positions than those of Bi2O2CO3. IfBi2O2CO3/Bi2WO6 composites are irradiated under visiblelight, the VB electrons of Bi2WO6 will be excited to CBdue to the narrow bandgap, leaving holes in VB. How-ever, for Bi2O2CO3, the VB electrons may not be excitedas its bandgap is 3.28 eV. The photoexcited electrons ofBi2WO6 then transfer to the CB of Bi2O2CO3 because ofthe internal field resulted from the potential of band energydifference, leaving holes in Bi2WO6. Therefore, the recom-bination of electrons and holes in Bi2WO6 is inhibited,leading to a higher quantum yield. It has been reported

Fig. 11. Schematic illustration of the proposed possible mechanismfor photodegradation of MB over Bi2O2CO3/Bi2WO6 heterojunctions.

that the VB potential of Bi2WO6 (3.0 V vs. NHE) ismore positive than that of �OH/OH− (1.9 V vs. NHE) and�OH/H2O (2.73 V vs. NHE) [28]. Therefore, the holes onthe Bi2WO6 surface could oxidize OH− and H2O, result-ing in �OH for MB degradation. On the other hand, forboth Bi2WO6 and Bi2O2CO3, the CB potentials are morepositive than that of O2/

�O−2 (−0.33 V vs. NHE) [28, 29],

indicating that �O−2 could not be generated from the one

electron reduction of O2 on the Bi2O2CO3/Bi2WO6 hetero-junctions. The possible photocatalytic reactions are illus-trated as follows:

Bi2WO6+hv→ Bi2WO6�h++ e−� (2)

Bi2WO6�e−�+Bi2O2CO3 → Bi2WO6+Bi2O2CO3�e

−�(3)

Bi2WO6�h+�+H2O→ Bi2WO6+�OH+H+ (4)

Bi2WO6�h+�+OH− → Bi2WO6+�OH (5)

MB+�OH→Degraded products (6)

It should be noted that the as prepared sample with aBi2O2CO3 mass fraction of 0.31 shows lower photocat-alytic efficiency than that with a Bi2O2CO3 mass frac-tion of 0.18, indicating that over coupled Bi2O2CO3 maydecrease the photocatalytic activity of Bi2O2CO3/Bi2WO6

heterojunctions. We considered that the detrimental effectof the excess Bi2O2CO3 coupling content could beascribed to the following reasons. Firstly, the excesscoupled content of Bi2O2CO3 may reduce the visiblelight harvest of heterojunctions, leading to the decreaseof photogenerated carriers and thus, low quantum yield.Secondly, the excess coupled content of Bi2O2CO3 in thecomposites may decrease the active sites for oxidation ofMB, as �OH are generated on the Bi2WO6 surface.

4. CONCLUSIONSHierarchical flower-like Bi2O2CO3/Bi2WO6 heterojunc-tions with large specific surface areas and well-definedinterfaces have been successfully prepared via an one-pot hydrothermal approach. The decomposition of ureaunder hydrothermal condition is the reason for the gener-ation and in situ carbonization of Bi2WO6, which leads tothe formation of Bi2O2CO3/Bi2WO6 heterojunctions withwell-defined interfaces. Meanwhile, the selective adsorp-tion of SDS on the (001) planes of Bi2WO6 nuclei isresponsible for the growth of Bi2WO6 nanoplates and thesubsequent self-assembly of those nanoplates into hierar-chical flower-like structures. The hierarchical flower-likeBi2O2CO3/Bi2WO6 heterojunctions show enhanced photo-catalytic activities as compared to the flower-like Bi2WO6

and Bi2WO6 prepared in the absence of SDS for MBdegradation, which may be due to the larger surface areasand enhanced charge separation at the heterojunction inter-faces. Bi2O2CO3 acts as a trapper of the photogenerated





Article

electrons from Bi2WO6, improving the quantum yield ofBi2WO6.

Ethical ComplianceThere are no researches conducted on animals or humans.

Conflicts of InterestThere are no conflicts to declare.

Acknowledgments: The authors acknowledge thefinancial support from The China Scholarship Council(Grant No. 201708430181).

References and Notes1. Fujishima, A. and Honda, K., 1972. Electrochemical photolysis of

water at a semiconductor electrode. Nature, 238(5358), pp.37–38.2. Xu, C., Anusuyadev, P.R., Aymonier, C., Luque, R. and Marre, S.,

2019. Nanostructured materials for photocatalysis. Chemical SocietyReviews, 48(14), pp.3868–3902.

3. Liang, W., Pan, J., Duan, X., Tang, H., Xu, J. and Tang, G., 2020.Biomass carbon modified flower-like Bi2WO6 hierarchical architec-ture with improved photocatalytic performance. Ceramics Interna-tional, 46(3), pp.3623–3630.

4. Cheng, J., Shen, Y., Chen, K., Wang, X., Guo, Y., Zhou, X. andBai, R., 2018. Flower-like Bi2WO6/ZnO composite with excel-lent photocatalytic capability under visible light irradiation. ChineseJournal of Catalysis, 39(4), pp.810–820.

5. Wu, R., Song, H., Luo, N. and Ji, G., 2018. Hydrothermal prepa-ration of 3D flower-like BiPO4/Bi2WO6 microsphere with enhancedvisible-light photocatalytic activity. Journal of Colloid and InterfaceScience, 524, pp.350–359.

6. Fei, T., Yu, L., Liu, Z., Song, Y., Xu, F., Mo, Z. and Li, H., 2019.Graphene quantum dots modified flower like Bi2WO6 for enhancedphotocatalytic nitrogen fixation. Journal of Colloid and InterfaceScience, 557, pp.498–505.

7. Li, X., Huang, R., Hu, Y., Chen, Y. and Liu, W., 2012. A tem-plated method to Bi2WO6 hollow microspheres and their conversionto double-shell Bi2O3/Bi2WO6 hollow microspheres with improvedphotocatalytic performance. Inorganic Chemistry, 51(11), pp.6245–6250.

8. Shang, M., Wang, W., Zhang, L., Sun, S. and Wang, L., 2009.3D Bi2WO6/TiO2 hierarchical heterostructure: Controllable synthe-sis and enhanced visible photocatalytic degradation performances.The Journal of Physical Chemistry C, 113(33), pp.14727–14731.

9. Chaiwichian, S., Inceesungvorn, B., Wetchakun, K. andPhanichphant, S., 2014. Highly efficient visible-light-induced pho-tocatalytic activity of Bi2WO6/BiVO4 heterojunction photocatalysts.Materials Research Bulletin, 54, pp.28–33.

10. Xue, S., Wei, Z., Hou, X., Xie, W. and Li, S., 2015. Enhancedvisible-light photocatalytic activities and mechanism insight ofBiVO4/Bi2WO6 composites with virus-like structures. Applied Sur-face Science, 355, pp.1107–1115.

11. Jiang, Y., Chen, H.Y., Li, J.Y., Liao, J.F., Zhang, H.H., Wang,X.D. and Kuang, D.B., 2020. Z-scheme 2D/2D heterojunctionof CsPbBr3/Bi2WO6 for improved photocatalytic CO2 reduction.Advanced Functional Materials, 30(50), p.2004293.

12. Gao, Y., Liu, S., Wang, Y., Zhao, P., Li, K., He, J. and Liu, S.,2020. Fabrication of nitrogen defect mediated direct Z schemeg-C3Nx /Bi2WO6 hybrid with enhanced photocatalytic properties.Journal of Colloid and Interface Science, 579, pp.177–185.

13. Li, S., Chen, J., Hu, S., Wang, H., Jiang, W. and Chen, X., 2020.Facile construction of novel Bi2WO6/Ta3N5 Z-scheme heterojunc-tion nanofibers for efficient degradation of harmful pharmaceuticalpollutants. Chemical Engineering Journal, 402, p.126165.

14. Tang, Q.Y., Chen, W.F., Lv, Y.R., Yang, S.Y. and Xu, Y.H., 2020.Z-scheme hierarchical Cu2S/Bi2WO6 composites for improved pho-tocatalytic activity of glyphosate degradation under visible light irra-diation. Separation and Purification Technology, 236, p.116243.

15. Huang, X. and Chen, H., 2013. One-pot hydrothermal synthesis ofBi2O2CO3/Bi2WO6 visible light photocatalyst with enhanced photo-catalytic activity. Applied Surface Science, 284, pp.843–848.

16. Zhao, T., Zai, J., Xu, M., Zou, Q., Su, Y., Wang, K. andQian, X., 2011. Hierarchical Bi2O2CO3 microspheres with improvedvisible-light-driven photocatalytic activity. CrystEngComm, 13(12),pp.4010–4017.

17. Liu, Y., Wang, Z., Huang, B., Yang, K., Zhang, X., Qin, X. andDai, Y., 2010. Preparation, electronic structure, and photocatalyticproperties of Bi2O2CO3 nanosheet. Applied Surface Science, 257(1),pp.172–175.

18. Qiang, Z., Liu, X., Li, F., Li, T., Zhang, M., Singh, H. and Cao, W.,2021. Iodine doped Z-scheme Bi2O2CO3/Bi2WO6 photocatalysts:Facile synthesis, efficient visible light photocatalysis, and photocat-alytic mechanism. Chemical Engineering Journal, 403, p.126327.

19. Zhou, Y., Tian, Z., Zhao, Z., Liu, Q., Kou, J., Chen, X., Gao, J.,Yan, S. and Zou, Z., 2011. High-yield synthesis of ultrathin anduniform Bi2WO6 square nanoplates benefitting from photocatalyticreduction of CO2 into renewable hydrocarbon fuel under visiblelight. ACS Applied Materials & Interfaces, 3(9), pp.3594–3601.

20. Li, Y., Liu, J. and Huang, X., 2008. Synthesis and visible-light photo-catalytic property of Bi2WO6 hierarchical octahedron-like structures.Nanoscale Research Letters, 3(10), pp.365–371.

21. Li, Y., Liu, J., Huang, X. and Li, G., 2007. Hydrothermal synthesisof Bi2WO6 uniform hierarchical microspheres. Crystal Growth &Design, 7(7), pp.1350–1355.

22. Hao, Y., Li, F., Chen, F., Chai, M. and Liu, R., 2014. In situ one-stepcombustion synthesis of Bi2O3/Bi2WO6 heterojunctions with notablevisible light photocatalytic activities. Materials Letters, 124, pp.1–3.

23. Yu, C., Zhou, W., Zhu, L., Li, G. and Yang, K., 2016. Integratingplasmonic Au nanorods with dendritic like �-Bi2O3/Bi2O2CO3 het-erostructures for superior visible-light-driven photocatalysis. AppliedCatalysis B: Environmental, 184, pp.1–11.

24. Guan, M.L., Ma, D.K., Hu, S.W., Chen, Y.J. and Huang, S.M., 2011.From hollow olive-shaped BiVO4 to n–p core–shell BiVO4@Bi2O3

microspheres: Controlled synthesis and enhanced visible-light-responsive photocatalytic properties. Inorganic Chemistry, 50(3),pp.800–805.

25. Shi, J., Li, J., Huang, X. and Tan, Y., 2011. Synthesis and enhancedphotocatalytic activity of regularly shaped Cu2O nanowire polyhe-dra. Nano Research, 4(5), pp.448–459.

26. Dong, G., Ho, W. and Zhang, L., 2015. Photocatalytic NO removalon BiOI surface: The change from nonselective oxidation to selectiveoxidation. Applied Catalysis B: Environmental, 168, pp.490–496.

27. Sun, J., Chen, G., Wu, J., Dong, H. and Xiong, G., 2013. Bismuthvanadate hollow spheres: Bubble template synthesis and enhancedphotocatalytic properties for photodegradation. Applied Catalysis B:Environmental, 132, pp.304–314.

28. Sheng, J., Li, X. and Xu, Y., 2014. Generation of H2O2 and OHradicals on Bi2WO6 for phenol degradation under visible light. ACSCatalysis, 4(3), pp.732–737.

29. Zhang, Y., Li, D., Zhang, Y., Zhou, X. and Guo, S., 2014. Graphene-wrapped Bi2O2CO3 core–shell structures with enhanced quantumefficiency profit from an ultrafast electron transfer process. Journalof Materials Chemistry A, 2(22), pp.8273–8280.

Received: 1 December 2020. Accepted: 26 January 2021.


Materials Express - Ingenta Connect

Documents